The aim of the present research is to compare and contrast the human performance and alertness effects of 4 different nightly sleep durations (3, 5, 7, or 9 hours) across 7 consecutive days. Results will provide information regarding the rate at which recuperation occurs during sleep, and the differential effects that these various sleep durations have on that rate of recuperation. In this study, 64 healthy subjects (male and female) spend 15 consecutive days in the residential clinical research facility at the Johns Hopkins Bayview Medical Center's General Clinical Research Center. For the first 3 days, subjects are trained on the various performance measures and allowed to habituate to the research envrionment with 8 hours of sleep per night. Results from the 4th day of testing constitute baseline performance levels. Subjects are then allowed either 3, 5, 7, or 9 hours of sleep (n = 16 per sleep duration group) over the next 7 nights (i.e., Day 4 through Day 10). Recovery sleep (8 hours per night) occurs over the last 4 nights. Daytime measures (administered on a rigorous and consistent schedule across all days - training, baseline, experimental, and recovery) include simulated driving performance, various cognitive/psychomotor/mood tests from the Walter Reed Performance Assessment Battery, sleep latency tests, vitals signs, continuous recordings of polysomnographic variables (EEG, EKG, EMG, EOG), eye tracking, actigraphy, the Synthetic Work Task, and a Group Decision Task. Initial results indicate significant differences between groups on all performance measures during the 7 days which the 3-, 5-, 7-, and 9-hour sleep conditions are imposed. Further analyses will be performed to clearly delineate the relationship between actual sleep amounts across nights and subsequent daytime performance - information that will be used to refine the Walter Reed Sleep/Performance Model (SPM). The SPM will be used to enhance management of sleep and alertness during military operations, and could be used for similar purposes in various civilian settings (e.g., enhanced work/rest scheduling in the transportation industry).